The present invention relates to an apparatus, method, and medium which record and/or reproduce information on an optical information recording medium by using holography.
Through a Blu-ray Disc™ specification using a blue-violet semiconductor laser, at present, commercialization of optical disk having recording density of about 100 GB is performed also in consumer use. From now on, large capacity greater than 500 GB is expected also in an optical disk. However, for realizing the above-described ultra-high density by using an optical disk, a high-density technology is needed through a new method which is different from a high-density technology using conventional short wavelength and a high numerical aperture of objective lens.
Research about next-generation storage technology is performed, while a hologram recording technique in which digital information is recorded by using holography gathers attention. As the hologram recording technique, for example, JP-A-2004-272268 is disclosed. In this publication, a so-called angle multiple recording system is disclosed such that different page data is displayed on a spatial light modulator to perform multiple recording while changing an incidence angle to an optical information recording medium of a reference beam. In this publication, a technology is further disclosed such that when a signal beam is focused on a lens and an aperture (spatial filter) is arranged in a beam waist of the signal beam, a distance between adjacent holograms is made to be short.
As the hologram recording technique, for example, WO 2004/102542 is further disclosed. In this publication, an example of using a shift multiplexing system is disclosed. That is, in one spatial light modulator, a light beam emitted from internal pixels is used as a signal beam and a light beam emitted from external annular pixels is used as a reference beam, and both of luminous fluxes are condensed on an optical information recording medium by using the same lens. Near a focal plane of the lens, the signal beam and the reference beam are allowed to interfere with each other, thus recording a hologram.
As a method for adjusting a reproduction laser at the time of reproducing a hologram, for example. JP-A-2007-256949 is disclosed. In this publication, descriptions will be made as follows. That is, “a reference tilt hologram for specifying a reference incidence angle in the radial tilt direction is recorded in advance on a holographic memory medium. During recording and reproducing operations, the reference beam is emitted to a recording position of the reference tilt hologram and the reference incidence angle (reference angle Sr) of the reference beam in the radial tilt direction is detected based on a received light state. A tilt actuator 19 for displacing the holographic memory medium in the radial tilt direction is driven and controlled to adjust an incidence angle of the reference beam in the radial tilt direction to the reference angle Sr. Then, the signal beam and the reference beam are emitted to the holographic memory medium to perform the recording and reproducing operations”.